A variety of methods are currently available for making arrays of biological macromolecules, such as arrays of nucleic acid molecules or proteins. One method for making ordered arrays of DNA on a porous membrane is a “dot blot” approach. In this method, a vacuum manifold transfers a plurality, e.g., 96, aqueous samples of DNA from 3 millimeter diameter wells to a porous membrane. A common variant of this procedure is a “slot-blot” method in which the wells have highly-elongated oval shapes. The DNA is immobilized on the porous membrane by baking the membrane or exposing it to UV radiation. This is a manual procedure practical for making one array at a time and usually limited to 96 samples per array. “Dot-blot” procedures are therefore inadequate for applications in which many thousand samples must be determined.
An alternate method of creating ordered arrays of nucleic acid sequences is described by Pirrung, et al. (U.S. Pat. No. 5,143,854, 1992), and also by Fodor, et al. (Science 251:767-773, 1991). The method involves synthesizing different nucleic acid sequences at different discrete regions of a support. This method employs elaborate synthetic schemes, and is generally limited to relatively short nucleic acid sample, e.g., less than 20 bases. A related method has been described by Southern, et al. (Genomics 13:1008-1017, 1992).
Montgomery (U.S. Pat. No. 6,093,302, 2000) teaches a method for making arrays of polymers by employing electrochemically generated reagents that are confined by buffering and/or scavenging agents. The method requires substituting standard chemical reactions that can be used for polymer synthesis (e.g. oligonucleotide chemistry) with tailored electrochemical reactions.
There is a need in the art for a method of synthesizing high-density arrays of polymers that makes use of the many standard chemistries already described for synthesizing individual polymers, including enzymatic techniques. The current invention addresses this problem by making use a barrier to a reaction that can be selectively applied to different features in an array. The use of a barrier minimizes the need to tailor well understood chemical reactions to fit a specific requirement for constructing arrays (e.g. the use of photocleavable protecting groups).